1. Field of the Invention
The present invention relates to a heating element for use in a steering wheel of an automobile, a motor boat or the like, as well as to a steering wheel equipped with the heating element.
2. Background Art
For the comfort of those who drive automobiles, motor boats and the like in cold areas, steering wheels with heating elements have been put into practical use.
Some of the conventional heating elements for this application have been disclosed in, for example, Japanese Patent Laid-Open Application No. H4-15162, and Japanese Patent Laid-Open Application No. S61-81273, which are shown in FIG. 14 and FIG. 15.
A heating element 1 as shown in FIG. 14 comprises a heater 2 formed of a vertical knit stretch fabric, a textile 3 hemming the heater edge, and a connection wire 4 stretching to cover the entire width of the heater 2 for connecting the heater 2 with a power supply. Heating element 1 has been bonded to a cover 5 of a steering wheel.
A steering wheel 31 as shown in FIG. 15 comprises a core 32, a heat insulator 33 covering the core 32, and a heating element 34 is disposed on the outer periphery of heat insulator 33. The heating element 34 comprises a heater wire 35 and a power supply wire 36, and the power supply wire 36 supplies electric power. A connection 37 connecting the heater wire 35 with the power supply wire 36 is disposed at a rear part of a spoke 31a. A thermistor 38 for detecting the temperature of heating element 34 is disposed in a ring portion 31b. All these elements are covered with a steering wheel cover 39.
However, in the structure as shown in FIG. 14, where heating element 1 is bonded directly to a thin cover 5 of a synthetic resin sheet or a leather, fine heaters 2 of heating element 1 cannot withstand a heavy load. On the other hand, thick heaters 2 readily generate protrusions on a surface of the cover 5. This is a problem with the conventional heating elements.
Another problem is that, since the heater 2 is formed of a stretch fabric, connection wire 4 needs to be provided to cover the entire width of heater 2. Namely, there are quite a number of connection points, and it is difficult to connect all of the connection points without fail. This leads to a problem of low reliability.
Still another problem is that, although the edge is hemmed with a textile 3, the remainder of the heater 2 remains stretchable. So, the heater 2 may expand to a larger size when it is bonded to the cover 5, and it is not easy to attach it properly on the cover 5. Moreover, connection of heater 2 with connection line 4 is not an easy operation.
In a steering wheel as shown in FIG. 15, a connection 37 is disposed on the reverse surface of the spoke 31a. This creates a protrusion on the surface of the steering wheel 31. The thermistor 38 is disposed in the ring portion 31b, and is also a cause of a protrusion on the surface of the steering wheel 31. The protrusions are not only uncomfortable to a driver handling the steering wheel, but they provide a disadvantage with respect to the appearance of the steering wheel.
Furthermore, the thermistor 38 detects different temperatures depending on whether a driver is gripping the steering wheel in a vicinity of the thermistor 38 or not. Therefore, stable temperature control can not be expected.
If the core 32 is provided with recesses for housing the connection 37 and the thermistor 38 in order to improve the driver's feeling and appearance of the steering wheel, the core 32 needs to be provided with different designs depending on whether the steering wheel will include a heating element. In other words, the core 32 cannot be of a certain standard design cannot be of a certain standard design that is common for the production of all steering wheels, and this leads to a difficulty in providing steering wheels at a low cost.
The present invention addresses the above-described problems and aims to provide a heating element for steering wheels which does not generate a protrusion on the surface of the cover material due to the presence of a heater, a connection or the like constituent members. The heating element also has high durability and high reliability in the connection between the connection wire and the heater, and can be attached easily to a steering wheel. The present invention also provides a steering wheel equipped with the heating element.
A steering wheel in accordance with the present invention does not give any uncomfortable feeling to a driver handling the steering wheel, and has a good appearance. Furthermore, cores of a certain standard design can be used in common for the production of all steering wheels, regardless of the existence of the heating element. Thus an inexpensive steering wheel can be provided.